In mathematics a **quadric**, or **quadric surface**, is any D-dimensional (hyper-)surface represented by a second-order equation in spatial variables (coordinates). If the space coordinates are , then the general quadric in such a space is defined by the algebraic equation

The normalized equation for a three-dimensional (D=3) quadric centred at the origin (0,0,0) is:

- ellipsoid:
- spheroid - special case of ellipsoid
- sphere - special case of spheroid:
- elliptic hyperboloid
- elliptic paraboloid:
- hyperbolic paraboloid of one sheet:
- hyperbolic paraboloid of two sheets:
- cone:
- cylinder:

External links:

- http://www.geom.uiuc.edu/docs/reference/CRC-formulas/node61.html,
*16 Quadrics*in*Geometry Formulas and Facts*by Silvio Levy, excerpted from 30th Edition of the CRC Standard Mathematical Tables and Formulas (CRC Press).